An electrophotographic light-sensitive material generally comprises a support in which at least the surface is electrically conductive, and at least one layer of a photoconductive composition on the support. In some cases an intermediate layer composed of a polymeric substance is provided between the electrically conductive surface of the support and the photoconductive composition layer to improve adhesion and/or as a barrier layer. Polymeric substances which can be used for the intermediate layer are described, for example, U.S. Pat. Nos. 3,640,708, 3,438,773, 3,745,005 and 3,932,179.
Polymeric substances for use in the intermediate layer are, as described in the above references, addition polymerization type hydrophobic/water-insoluble copolymers, such as terpolymers and tetrapolymers, containing a constituent repeating unit derived from a carboxylic group, e.g., carboxylic group of itaconic acid or acrylic acid, and/or a constituent repeating unit derived from vinylidene chloride. The term "constituent repeating unit" is used herein according to the definition described in Kobunshi (High Polymers), Vol. 27, pp. 345 to 359 (1978) (Japanese version of Pure and Applied Chemistry, Vol. 48, pp. 373 to 385 (1976).
It has been found that while good adhesion between the electrically conductive surface of the support and the photoconductive composition layer can be attained by using such hydrophobic/water-insoluble terpolymers or tetrapolymers in the intermediate layer they exert serious adverse effects on the electrical and photoconductive properties of the photoconductive composition layer. In particular such terpolymers or tetrapolymers containing an acid component (e.g., itaconic acid or acrylic acid) or a constituent repeating unit derived from vinylidene chloride which is liable to release hydrogen chloride on decomposition seriously deteriorate electrical properties.
U.S. Pat. Nos. 3,647,432, 3,765,884, etc., disclose compositions comprising organic photoconductive compounds or sensitizers and various binder substances. There are many useful binder substances, including polycondensation polymers (polyesters) of ethylene glycol or neopentyl glycol and terephthalic acid or isophthalic acid. It has been found, however, that although the polyester can be used as a binder substance for a photoconductive composition, when it is present as a single binder component for an organic photoconductive composition it happens to degrade the electrical properties of the photoconductive composition, making it impossible to easily receive an initial electrostatic charge (i.e., 600 volts or more) within the preferred handling range of the photoconductive composition.
Japanese Patent Application (OPI) No. 153741/77 (the term "OPI" is used herein to refer to a "published unexamined patent application") discloses the use of amorphous, water-insoluble and non-linear polyesters or copolyesters as binders for a photoconductive composition layer of a multi-layer composite photoconductive element (electrophotographic material) comprising a support having an electrically conductive layer and the photoconductive composition layer on the support which are electrically in contact with each other, or for the preparation of an intermediate layer which is, if necessary, provided between the support (electrically conductive layer) and the photoconductive composition layer. This electrophotographic light-sensitive material has the features that the electrical and electrophotographic properties of the photoconductive composition layer are superior, adhesion between the photoconductive composition layer and the electrically conductive layer of the support or intermediate layer is good and the film properties of the photoconductive composition layer are good.
As a result of extensive studies on the electrophotographic light-sensitive material disclosed in Japanese Patent Application (OPI) No. 153741/77--as that material has good electrophotographic properties and the photoconductive composition thereof has good electrophotographic, electrical and film properties--it has been surprisingly found in accordance with the present invention that a photoconductive composition having excellent electrical, electrophotographic and film properties can be prepared using inexpensive and relatively low molecular weight linear copolyesters which have heretofore been believed unsuitable for use as reinforcing agents or binders for photoconductive compositions for the reasons that they have low solubility in general solvents, high crystallizability and have poor adhesive force to other substances. It has further been found that an electrophotographic light-sensitive material with a photoconductive composition layer prepared using the above photoconductive composition has excellent electrophotographic properties.